My major interest is what distinguishes a theoretically possible and impossible language. In the present days, it is said that there are thounsands of languages spoken on the Earth, and they are astonishingly divergent. On the other hand, there might be also "impossible" languages that are not included in such divergence. Then, what is the qualitative difference between them? Is there a border between them? Where? Or, such border might not exist. As one of the approaches to my research interest, recently, I have been working on a topic of linguistic complexity .
Linguistists have generally accepted the statement, "any langauge is not simpler or more complex than another but equally complex," which is called equi-complexity of language. In fact, it has been reported that when two languages are compared, one of the langauges are sometimes more complex in a subdomain, say morphology; the other one is more complex in another subdomain, say syntax. However, no one has not yet been verified whether the equi-complexity of language is true or not, which some linguists have begun to study after the end of 20th century, when technical issues started to be solved. With the topic, I am working on the question, "Are the complexities of every possible language among a definite range, or doesn't there such range exist?" through mathematical modeling based on information theory and measure theory.